Well..it's time for a 3rd edition.
After going through Chapter 1 to 7, I found
that this is a good book on the subject "lex & yacc".
Unfortunately, the examples in the book (Chap 1 to 5) do not
compile and link properly. Even if an example happens to compiled and linked
successfully, the executable will crash when executed :(
(i.e. Example 1-7 (pg. 17))
I felt that failure in compiling and linking the examples
will discourage lex & yacc newbies from experimenting and learning lex & yacc.
I've included some fixes below to make the examples compile and link properly.
(I'm using Cygwin on W2K, flex 2.5.4 and bison 1.875)
Hopefully, these fixes will help lex & yacc newbies who is reading
this book and tinkering with the examples and exercises.
-Andy Wong Man Boon (Email me at andyw_apcd@hotmail.com
if you want fixes for the other examples)
{15} to {18}
For ch1-05.l, add...
%{
...
int lookup_word(char *word);
int add_word(int type, char *word);
/* We do not require yyunput so do not define it to avoid
'C' compiler warning */
#define YY_NO_UNPUT
%}
%option noyywrap
%%
...
%%
...
int add_word(int type, char *word) {...}
int lookup_word(char *word) {...}
For ch1-05.y, add..
%{
#include <stdio.h>
/* prototype for lexer function */
int yylex(void);
/* prototypes for error handling functions */
int yyerror(char *s);
%}
...
%%
...
%%
...
int main(void)
{
yyin = stdin; /* Initialise yyin ! */
...
return 0;
}
int yyerror(char *s)
{
fprintf(stderr, "yyerror: %s\n", s);
return 1; /* Recovery not attempted */
}
Compile ch1-05.l and ch1-05.y as follows:-
flex ch1-05.l
bison -y -d ch1-05.y
gcc -Wall -c lex.yy.c y.tab.c
gcc -Wall -o ch1-05 lex.yy.o y.tab.o
{24}
For Ex1-10.l, the returning values from
yylex() would be clearer if you add...
%{
#include <stdio.h>
...
#define YY_NO_UNPUT
%}
%option noyywrap
%%
...
\n { return '\n'; }
"$" { return 0; /* end of input */ }
%%
int main(void)
{
int val;
while( (val=yylex()) > 0) {
printf("token is %d\n", val);
}
printf("token is %d\n", val);
return 0;
}
Compile Ex1-10.l as follows:-
flex Ex1-10.l
gcc -Wall lex.yy.c -o Ex1-10
{59}
For ch3-01.y, the returning value of yyparse()
would be clearer if you add to the main() the following:-
int main(void)
{
...
bRet = yyparse();
if( bRet != 0) {
printf("yyparse() error: ret %d\n", bRet);
} else {
printf("yyparse() ok: ret %d\n", bRet);
}
return 0;
}
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